The old phrase "The enemy of my enemy is my friend" almost applies to this rare alliance of Microsoft and the Linux Foundation, which issued a joint letter to the American Law Institute (ALI) last week regarding the institute's draft "Principles of the Law of Software Contracts." The joint letter was made public on Sunday.

At stake for software makers -- both open source and commercial -- is how software contracts are likely to be interpreted and adjudicated in the future.

The ALI is holding its annual meeting this week in Washington, and on the agenda is a move to finalize the draft, which "presents legal principles to guide courts in deciding disputes involving transactions in software and to guide those drafting software contracts," according to a statement on the ALI's Web site. Among those are discussions of topics such as software warranties.

Both open source advocates and Microsoft (NASDAQ: MSFT) feel left out of the process.

It's the likelihood that document will be approved at this week's meeting that brought the Linux Foundation and Microsoft together to request more time to study the document and to provide their own feedback to the ALI's Principles. "We have asked the ALI to allow more time for comment from interested parties reflecting the wide range of software developers and users," said the joint letter.

So who or what is the ALI?

The ALI is an influential, decades old organization of lawyers who work "to promote the clarification and simplification of the law and its better adaptation to social needs, to secure the better administration of justice, and to encourage and carry on scholarly and scientific legal work," according to the group's description of its activities.

Much of that work encompasses "restatement of basic legal subjects that would tell judges and lawyers what the law was," the description said.

The alliance, however, responds with the cry of "Don't leave us out."

"The principles outlined by the ALI interfere with the natural operation of open source licenses and commercial licenses as well by creating implied warranties that could result in a tremendous amount of unnecessary litigation, which would undermine the sharing of technology," wrote Jim Zemlin, executive director of the Linux Foundation, in a blog post.

The fact that these two "blood enemies" could collaborate to attack the ALI draft is an indication of how dire they believe the situation could become -- especially in light of recent history.

Microsoft executives are famous for their many pronouncements over the years, referring to Linux as a "cancer," and company executives as recently as two years ago warned Linux vendors that they were infringing some 235 Microsoft patents.

Those earlier claims reverberated anew last winter when Microsoft sued GPS device maker TomTom for infringing multiple patents, three of which involve file storage technologies used by the company's Linux variant that the devices run on. Microsoft claims it owns those patents and thus, many Linux supporters believe a legal onslaught from the software giant is only a matter of time.

In the case last winter, TomTom countersued Microsoft but later settled the tet-a-tet quietly with a check and a license for Microsoft's intellectual property. The threat of further lawsuits which could undermine Linux still simmers on open source developers' back burners, though. That makes the alliance between Microsoft and the Linux Foundation seem even more implausible but understandable.

"Our industry is diverse and sometimes contentious, but if nothing else unites us it is that we all believe in the power of software," the joint letter said.